This book constitutes the refereed proceedings of the 12th International Conference on Flexible Query Answering Systems, FQAS 2017, held in London, UK, in June 2017.The 21 full papers presented in this book together with 4 short papers were carefully reviewed and selected from 43 submissions. The papers cover the following topics: foundations of flexible querying; recommendation and ranking; technologies for flexible representations and querying; knowledge discovery and information/data retrieval; intuitionistic sets; and generalized net model.